In general, an air suspension unit mounted on a vehicle has a leveling valve that controls the supply and exhaust of compressed air through an air spring. Such air springs are typically installed between a vehicle axle and a vehicle body. The air springs respond according to changes in the level position of a moving vehicle. Common leveling valves can be classified as either a rotary type or a plunger type according to the operational method thereof.
A conventional plunger type valve includes a flow path that passes in a vertical direction between an inlet and an outlet. Compressed air is let in and out and transferred between left and right air springs by a plunger that moves caps, thereby opening different passageways. The plunger is moved in response to a lever that is typically connected between the axle and the vehicle body.
In use, when the axles move up, the rising rotation of the lever turns a rotor, which correspondingly lifts up the plunger. As the plunger is raised, the lower cap opens the flow path to communicate with the connecting path.
As a result, the high pressure of compressed air pushes the upper cap down and the air flows into the flow path through the inlet. The compressed air is then supplied to the left and right air springs through a lower cap and a connecting path.
When the axles move down, the rotor is turned with the falling rotation of the lever. Rotation of the rotor lowers the plunger. The falling movement of the plunger causes the lower cap to block the flow path via the restoration force of the return spring, thereby disconnecting the communication with the inlet.
In the leveling valve design, the inlet and the outlet open or close according to the rotational angle of the lever when the wheel axles move up or down. There is only a constant change in the flow amount of compressed air per hour depending on the change in the rotational angle of the lever so that the time taken for compressed air to flow in and out of the air springs cannot be adjusted according to the degree of change in the level position of a moving vehicle.
There are drawbacks in the related art. In the related art designs, vehicle rolling is not restrained within a short time interval. Therefore, the turning stability and the response speed of a vehicle are negatively affected.